Kelly Macdonald caught the Coen brothers on the hop. Having convinced the casting director of the Coens’ new film, No Country For Old Men, that she could pull of an authentic West Texas accent, the 31-year-old Glaswegian actress was presented to the notoriously perfectionist, and evidently deeply misgiving, filmmaker siblings.

‘I think the casting director surprised them by bringing me in for an audition,’ says the currently heavily pregnant Macdonald, ‘because they wanted to cast as close to the area the film is set in as possible, and I’m as far away as you can get from a West Texas person. So they were a bit nonplussed. Ethan was quite chatty, but Joel, I think, thought it was a big waste of time. Then I read the first scene, and it was all lovely after that. They were surprised by the accent, and that I was able to keep it going. Auditions can be mortifying experiences but every so often things just gel and it goes well.’

In the film, which is based on Cormac McCarthy’s superb hardboiled crime novel, Macdonald plays Carla Jean, the sweet trailer trash wife of coarse but loving husband Llewelyn Moss (Josh Brolin), who gets into trouble when he steals a bag full of money from a Tex-Mex border drug deal gone wrong. With Llewelyn on the run from a psychotic killer (a terrifying Javier Bardem), Carla Jean is torn between protecting her man from the law and handing him over for safe keeping to the weary but decent local sheriff (sleepy-eyed Tommy Lee Jones).

It’s a brutal, blackly comic, brilliantly made film, and there’s great satisfaction to be derived from the filling in of blanks its extraordinarily spare style requires of the audience. ‘Cormac McCarthy can afford to be sparse with dialogue,’ Macdonald says, ‘because he’s so clever. Not a lot of people can put across what he does in just a couple of sentences. So Carla Jean’s character was very apparent. I had an understanding of her, and it turned out that wasn’t so far away from Joel and Ethan’s understanding of her. I didn’t think she was just the little woman who would do anything for her man,’ says Macdonald. ‘I don’t have a huge amount of screen time compared to the boys, but the scenes I’ve got are with all three leads, and they don’t even all share screen time together. They’re really good scenes,’ Macdonald concludes. ‘It’s the best part I’ve ever had.

‘The Coen brothers are really nice guys, and they’re very funny, in a quiet way. They know exactly what they’re after. They spend so long working on a script, and they gather the right people around them. So by the time you arrive on the set it’s all good to go. They do all the hard work so you don’t have to.’

Macdonald had a similarly rewarding experience working with her leading men, Tommy Lee Jones in particular. The famously curmudgeonly Jones apparently felt likewise, proving instrumental in getting his diminutive Scottish co-star cast alongside him in veteran French filmmaker Bertrand Tavernier’s forthcoming adaptation of James Lee Burke’s Deep South-set crime novel, In the Electric Mist with Confederate Dead. ‘Tommy had a lot to do with the casting process,’ Macdonald says, ‘so it was nice to be asked back after having worked with him once. He’s not a figure of fear, but he’s got quite a reputation. I found him to be a very generous actor.’

She learned a lot about her trade working with Jones and the Coens, Macdonald says. In fact, she’s been getting an education on the job ever since making her debut in Trainspotting just over ten years ago. ‘I was so lucky to get Trainspotting,’ she recalls of giving up bar-maiding to play naughty schoolgirl Diane. ‘I hope I’m improving as years go by, because every job you get you’re working and learning from new people. It’s been quite a gradual learning curve. But I’m in my 30s now, and it’s nice to be somewhere where I feel I should be.’

Following the auspicious debut that won her a BAFTA Scotland nomination, Macdonald went straight into a leading role as a young London prostitute in the gritty drama Stella Does Tricks. Her career has since comprised substantial supporting roles in various significant films: Elizabeth, Gosford Park, Finding Neverland (in which she was perfectly cast as Peter Pan) and the acclaimed BBC political thriller State of Play.

Macdonald enjoyed a particularly fruitful year in 2005, appearing in no less than five films including the Richard Curtis-penned politics-tinged romance The Girl in the Café for which she was nominated for a Golden Globe award and won an Emmy. Since then, however, we haven’t seen her on either the big or small screens.

‘There’s always a break,’ Macdonald says stoically. ‘I’ve gone up to a year thinking, “Crap! When’s the next film going to come along?” That’s just the way of things. It’s a really tricky industry, and there’s lots of competition. But I’ve got good representation, and I’ve been quite lucky. Beyond that there’s not much I can do about it. It becomes a way of life almost, because you can’t be working all of the time, and then there’s no balance when you are working – it’s all or nothing. It can be quite unhappy making.’

‘That’s why it’s important to have a settled home life, and I have a very happy home life,’ Macdonald says of her life in London shared with husband Dougie Payne (the bass player of Travis, whom she married in 2003). ‘When we’re together it’s a very happy home life, but he’s been away this whole month, which has been quite hard, and I’ve been travelling for work this year too. You just have to get on with it.’

2007 has been a busier year for Macdonald, which means we’ll be seeing a lot more of her on screen in 2008. She made three American films back-to-back – No Country For Old Men, In the Electric Mist and Choke, an adaptation of cult author Chuck Palahniuk’s blackly comic novel – and Macdonald thinks her mastering an American accent for the Coens may well lead to her making more films in America. ‘You kind of have to have that under your belt before you’re really considered properly for American movies,’ she says.

Nevertheless, she’s happy to take a break in 2008. ‘Workwise I’ve not got any plans. I’ve never got any plans. Also, I’ve got this to deal with,’ Macdonald says, patting her belly. ‘It’s six months. It’s cooking nicely. Anyway, I don’t really take time off; I’m given time off. If something comes up I respond to I’ll probably do it, but meanwhile I’m quite happy to be the little woman for my husband.’

No Country For Old Men is out on Fri 18 Jan. Release dates for In the Electric Mist and Choke to be confirmed.